A common type of orifice plate employed in ink jet printing apparatus consists of a plurality of glass capillaries bonded vertically in a suitable sheet material such as glass or an epoxy resin. Such sheets are fabricated with relative ease by the techniques disclosed in the Cone U.S. Pat. No. 4,112,436.
The exposed surfaces of the glass capillaries in orifice plates of the above type lie in the same plane as the supporting sheet. The surface of the glass capillaries and the supporting sheet are similar with respect to being wetted by ink jet printing inks. By reason of this fact, the periodic shutdowns of the ink streams through the orifice plate can result in wetting the surfaces surrounding the orifices. Over a period of time, the spreading of the ink and its subsequent evaporation builds up ink solids on the exposed surface of the orifice plate. This buildup of solids adversely affects the subsequent startups of the apparatus. In time, the ink solids can accumulate to the extent that they form a grounding path to the drop charging electrodes. When this occurs, the entire apparatus must be taken out of service for replacement and/or cleaning of the orifice plate.
There is a need in the art for ink jet orifice plates including glass capillaries which have a reduced tendency to deposit ink solids on the exterior surface of the orifice plate.